Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M12/00—Hybrid cells; Manufacture thereof
  • H01M12/04—Hybrid cells; Manufacture thereof composed of a half-cell of the fuel-cell type and of a half-cell of the primary-cell type
  • H01M12/06—Hybrid cells; Manufacture thereof composed of a half-cell of the fuel-cell type and of a half-cell of the primary-cell type with one metallic and one gaseous electrode
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/8605—Porous electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8817—Treatment of supports before application of the catalytic active composition
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0241—Composites
  • H01M8/0245—Composites in the form of layered or coated products
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/64—Carriers or collectors
  • H01M4/66—Selection of materials
  • H01M4/661—Metal or alloys, e.g. alloy coatings
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/64—Carriers or collectors
  • H01M4/66—Selection of materials
  • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8803—Supports for the deposition of the catalytic active composition
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/90—Selection of catalytic material
  • H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/08—Fuel cells with aqueous electrolytes
  • H01M8/083—Alkaline fuel cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• This invention relates to a current collector for a catalytic electrode and an electrochemical cell containing the electrode.
• electrochemical cells that have catalytic electrodes. Examples include, but are not limited to, fuel cells, metal-air battery cells, gas (e.g., hydrogen) generating cells, and electrochemical sensor cells. Examples of such cells are found in US Patent Nos. 5,242,565; 5,308,711 ; 5,378,562; 5,567,538; 5,707,499; 6,060,196; 6,461,761 ; 6,602,629; 6,91 1,278; 7,001,689 and 7,001,865; and in International Patent Publication No. WO 00/36677.
• An advantage of electrochemical cells with catalytic electrodes is that they can use one or more active materials that are not contained within cell or battery housings, thereby providing long use time (e.g., discharge capacity) with a cell having a minimum volume. For example, oxygen in the air or from another source outside the cell housing can be reduced by the catalytic electrode as part of the overall reaction of the cell.
• electrical characteristics e.g., operating voltage, power output, energy density, discharge capacity, charging efficiency, cycle life and fade
• storage characteristics e.g., leakage resistance, cost, environmental impact of waste disposal, and safety in manufacturing.
• the electrical characteristics of the electrochemical cell can be improved in a number of ways, including the use of a catalytic material having greater catalytic activity, increasing the electrical conductivity and reducing the internal resistance within the catalytic electrode.
• Catalytic electrodes can include an electrically conductive current collector in direct contact with the catalytic material of the electrode to reduce the internal resistance of the catalytic electrode.
• various means have been used to minimize the internal resistance of the catalytic electrode, such as means of providing corrosion resistance of the surface of the current collector in contact with the catalytic electrode and means of providing good contact between the current collector and the catalytic portion of the electrode.
• the current collector surface can be coated with a metal, alloy or compound that is more corrosion resistant than the underlying substrate material, particularly when the current collector is in contact with the catalytic portion of the electrode and the cell's electrolyte.
• the current collector surface can be coated with particles of a conductive material such as carbon black, graphite or metal in a binder. Examples of these efforts can be found in International Patent Publication No. WO 00/36,686; U.S. Patent Publication Nos. 2006/0204839, 2005/0221190 and 2002/0132158; and in U.S. Patent Nos. 6403517, 6120940, 4865925 and 4248682.
• one aspect of the present invention is an electrochemical cell including a catalytic electrode, a counter electrode, a separator disposed between the catalytic electrode and the counter electrode, and an aqueous alkaline electrolyte, all contained within a cell housing having one or more ports for the passage of a gas through the housing to or from the catalytic electrode.
• the catalytic electrode includes a first side facing the separator, a second side opposite the first side and in fluid communication with the one or more ports, a catalytic layer including a catalytic material capable of reducing oxygen, and a porous current collector at least partially embedded in the catalytic material.
• the current collector has a first side corresponding to the first side of the catalytic electrode and a second side corresponding to the second side of the catalytic electrode.
• the current collector includes a substrate with an electrically conductive protective metal surface layer in contact with the catalytic material on one of the first side and the second side and a coating including electrically conductive particles in contact with the catalytic material on the other of the first side and the second side.
• the current collector can be at least partially embedded in the catalytic material on the first side of the catalytic electrode.
• the protective metal surface layer can be in contact with the catalytic material on the second side of the current collector, with the coating in contact with the catalytic material on the first side of the current collector.
• the protective metal surface layer can be present on essentially the entire first side and essentially the entire second side of the current collector.
• the protective metal surface layer can be a distinct layer with a different composition than a portion of the substrate beneath the metal surface layer.
• the protective metal surface layer can include gold, platinum, palladium, silver or a combination thereof. In one embodiment the protective metal surface layer includes gold.
• the coating can include a binder.
• the binder can include a polymeric material.
• the polymeric material can include a fluoropolymer, a polyvinyl alcohol or a combination thereof.
• the polymeric material includes a fluoropolymer, a polyvinyl alcohol or both a fluoropolymer and a polyvinyl alcohol.
• the electrically conductive particles can include carbon particles, gold particles, nickel particles, silver particles or a combination thereof.
• the conductive particles include graphite particles, carbon black particles or a combination of graphite particles and carbon black particles.
• the catalytic material can include a manganese oxide, an activated carbon, platinum, palladium, a cobalt oxide, a nickel oxide, an organic macrocyclic compound or a combination thereof. In some embodiments the catalytic material includes a manganese oxide, an activated carbon or a combination of a manganese oxide and an activated carbon.
• the electrolyte can include potassium hydroxide, sodium hydroxide or a combination of potassium hydroxide and sodium hydroxide.
• the catalytic electrode can be an oxygen reduction electrode for reducing oxygen from outside the cell housing.
• the cell can be a metal-air cell, the catalytic electrode is a positive electrode, and the counter electrode is a negative electrode comprising a metal as an active material.
• the active material of the negative electrode comprises zinc or an alloy of zinc.
• the cell can be a fuel cell.
• a second aspect of the invention is a process for making an electrochemical cell comprising the steps: (a) forming a current collector sheet by providing a sheet of a porous, electrically conductive metal substrate having a first side and a second side opposite the first side, forming an electrically conductive protective metal surface layer on at least a portion of the substrate, and forming a coating comprising electrically conductive particles and a binder on a portion of the substrate; (b) forming a catalytic electrode sheet with a first side and a second side opposite the first side by combining the current collector sheet with a catalytic material comprising a binder and a catalyst capable of reducing oxygen such that the first side and second sides of the current collector correspond to the first and second sides, respectively, of the catalytic electrode sheet, the current collector is at least partially embedded in the catalytic material, at least a portion of the coating is on the first side of the current collector and is in contact with the catalytic material, and at least a portion of the electrically conductive protective
• the current collector sheet can combined with the catalytic material after the oxygen diffusion layer is secured to the second side of the catalytic electrode sheet.
• the current collector sheet can be combined with the catalytic material by pressing the current collector sheet into a catalytic sheet including the catalytic material.
• the electrically conductive protective metal surface layer of the current collector sheet can be formed by plating a protective metal onto a surface of the substrate.
• the electrically conductive protective metal surface layer can extend over essentially the entire substrate sheet, or the electrically conductive protective metal surface layer can extend over only a portion of the substrate sheet.
• the coating can be formed by applying the coating to one side of the substrate such that the protective metal surface layer of the current collector is exposed on at least a portion of an opposite side of the current collector.
• the process according to the second aspect of the invention can be used to make the electrochemical cell according to the first aspect of the invention.
• FIG. 1 is an elevational view, in cross-section, of a portion of a catalytic electrode according to one embodiment
• FIG. 2 is an elevational view, in cross-section, of an embodiment the current collector in the portion of the catalytic electrode embodiment shown in FIG. 1.
• FIG. 3 is an elevational view, in cross-section, of a prismatic shaped metal-air cell with the catalytic electrode shown in part in FIG. 1 ;
• FIG. 4 is a graph showing discharge voltage as a function of time for zinc-air cells with current collectors plated with gold and unplated current collectors.
• An electrochemical cell according to the present invention includes a catalytic electrode.
• the catalytic electrode can be an electrode in which a gas such as oxygen is reduced or a gas such as hydrogen or oxygen is produced.
• oxygen from an external source is used as an active material that is reduced by a catalytic material in the presence of an aqueous alkaline electrolyte. Examples include fuel cells, metal-air cells and air-assisted cells.
• oxygen, hydrogen or another gas can be generated at the catalytic electrode in the presence of an aqueous alkaline electrolyte.
• a cell with an oxygen reduction catalytic electrode and an aqueous alkaline electrolyte can be used as an oxygen sensor due to the current produced by the cell being proportional to the quantity of oxygen reaching the catalytic electrode.
• a cell according to the invention includes a catalytic electrode, a counter electrode, a separator disposed between the catalytic electrode and the counter electrode and an aqueous alkaline electrolyte, all contained within a cell housing.
• the cell housing has at least one inlet/outlet port through which a gas can enter the cell and react within the catalytic electrode or through which a gas produced within the cell can exit the cell.
• the catalytic electrode includes a catalytic layer and a porous current collector at least partially embedded in the catalytic layer. As used herein, embedded means that at least a portion of the current collector is disposed below a surface of the catalytic layer.
• the current collector can be embedded by any suitable process, such as by pressing the current collector into the catalytic layer or by forming the catalytic layer partially or completely around the current collector.
• the catalytic layer includes a catalytic material containing a suitable catalyst capable of catalyzing reactions in the catalytic electrode in the presence of an aqueous alkaline electrolyte, such as the reduction of oxygen to produce hydroxyl ions or the oxidation of hydroxyl ions to produce oxygen.
• the catalytic material can include an electrically conductive material.
• the catalytic material can include a binder.
• particles of the catalyst are disposed on the surfaces of particles of a conductive material.
• catalysts include metal oxides such as manganese oxides, cobalt oxides and nickel oxides; carbons such as activated carbons and carbon blacks; metals such as platinum and palladium; and organic macrocyclic compounds such as cobalt tetramethoxyphenyl porphyrin and cobalt tetrphenyl porphyrin.
• conductive materials include carbons such as activated carbons, carbon blacks, graphitic carbons and carbon nano tubes.
• binder materials include fluoropolymers such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) and polyvinylidene fluoride (PVDF).
• One side of the catalytic electrode faces away from the counter electrode and is in fluid communication with the gas inlet/outlet port(s) in the cell housing.
• the opposite side of the catalytic electrode referred to as the separator side, is adjacent to the separator and faces toward the separator and the counter electrode.
• the current collector has an electrically conductive substrate and two opposite sides that, when embedded in the catalytic layer, correspond to the port side and the separator side of the catalytic electrode (i.e., the port side of the current collector is in fluid communication with the gas port(s), and the separator side of the current collector faces the separator and the counter electrode).
• One side of the current collector has an electrically conductive, protective metal surface layer to provide resistance to corrosion when in contact with the electrolyte and good electrical contact with the catalytic material. At least a portion of the current collector has a coating including electrically conductive particles. Preferably essentially the entire separator side and essentially the entire port side of the current collector are covered by at least one of the protective metal surface layer and the coating. As used herein, essentially the entire side or essentially all of a side means the entire side except for possible pinholes, small voids, cracks and other common imperfections in manufacturing.
• both the separator side and the port side of the current collector are covered by the protective metal surface layer, and a portion of the protective metal surface layer (e.g., the separator side or the port side) is covered by the coating.
• the protective metal surface layer does not cover the entire current collector, and at least those portions of the separator and port sides of the current collector that do not include the protective metal surface layer are covered by the coating.
• the protective metal surface layer can be disposed over the entire port side and the entire separator side of the current collector, with a coating of electrically conductive particles applied to a major portion of the separator or the port side.
• the protective metal surface layer does not extend under the entire area coated with the electrically conductive particles.
• the protective metal surface layer is exposed to the catalytic material and electrolyte on at least a portion of the separator, port or both sides of the current collector, and the coating is present and exposed to the catalytic material on at least a portion of at least one side of the current collector.
• the port side of the catalytic electrode can have a hydrophobic gas diffusion layer that is permeable to gas but impermeable to liquid water, thereby preventing electrolyte leakage from the cell.
• the hydrophobic layer can be formed from a hydrophobic mixture, such as a mixture including a high concentration of a hydrophobic material such as a fluoropolymer, or it can be a microporous hydrophobic film. Examples of such films include fluoropolymer films such as polytetrafluoroethylene and fluorinated ethylene propylene films.
• FIG. 1 is a cross-sectional view of a portion of a catalytic electrode.
• the electrode 120 has a catalytic layer 121 into which a current collector 123 is embedded.
• the electrode 120 can also include a gas diffusion layer 122 on the port (lower) side of the electrode 120.
• the upper side of the electrode 120 is the separator side.
• FIG. 2 is a cross-sectional view of an embodiment of the current collector 123 in the same orientation as in FIG. 1.
• the lower surface corresponds to the port side of the electrode 120, and the upper surface corresponds to the separator side of the electrode 120.
• the current collector 123 includes a substrate 140 with a layer 142 having a hydrogen overpotential higher than copper on both the port side and the separator side of the current collector.
• the current collector 123 also has a coating 144 of conductive particles over the layer 142 on the separator side of the current collector 123.
• the layer 142 is primarily only on the port side of the current collector 123, and the coating 144 is primarily only on the separator side of the current collector.
• the current collector substrate is a good electrical conductor.
• Suitable materials for the substrate include electrically conductive metals and metal alloys such as steel, stainless steel, nickel, copper, brass, tin, silver, gold, platinum, palladium and titanium.
• Metals such as steel, stainless steel, nickel, copper, brass and tin can be advantageous in some embodiments due to lower cost or ease of manufacture.
• Metals as gold, platinum and palladium can be advantageous in other embodiments because of their resistance to corrosion when in contact with the cell electrolyte.
• Other suitable substrate materials include electrically conductive metal oxides such as tin oxide and chromic oxide, and electrically conductive polymers such as polyaniline and polypyrrole.
• the substrate can have a core of one material covered with a layer of one or more suitable electrically conductive materials.
• the core is an electrically nonconductive material such as a plastic.
• the current collector substrate would be an excellent conductor of electricity, completely inert when in contact with the catalytic material and electrolyte in the electrode, inexpensive and easy to manufacture. However, no single material has all of these ideal characteristics. If the substrate material has sufficient electrical conductivity and resistance to corrosion and dissolution, its surfaces are considered to constitute a protective layer, and no additional protective layer may be required.
• a separate protective metal surface layer can be applied to at least those portions of the port side and the separator side that will not be coated with the electrically conductive particles.
• a metal that can also serve as a catalyst for the desired reaction in the catalytic electrode can be advantageous.
• Preferred materials for the protective metal surface layer are gold, platinum, palladium and silver, with gold being the most preferred. Because the materials for this added layer can be expensive, it can be advantageous to make this layer very thin, yet thick enough to provide a continuous layer through which the underlying substrate is not exposed.
• the protective metal surface layer is at least 0.01 ⁇ m thick and more preferably at least 0.1 ⁇ m thick.
• the protective metal surface layer is no more than 100 ⁇ m thick and more preferably no more than 10 ⁇ m thick.
• the current collector substrate can be further treated, such as by etching or sand blasting to roughen the surface, either before or after adding the protective layer, to minimize the electrical resistance between the current collector and the active material layer.
• the current collector is a porous structure that will allow water and ions to pass therethrough.
• suitable structures include wires, filaments, nonwoven mats, woven screens and fabrics, expanded metals, foams, porous sintered structures and the like.
• Preferred structures are wires, filaments, screens and expanded metals. Screens and expanded metals can be advantageous because they can be easily handled and embedded into the catalytic layer of the electrode without damage. Examples of metal screens that can be used include woven wire cloths.
• the wires can be cross-bonded (welded where they cross).
• the screens can have 50 to 50 openings per inch with wire diameters of 0.10 to 0.15 mm. Such woven wire cloths are available from Gerard Daniel Worldwide, Fontana, California, USA.
• Expanded metals are of a one-piece structure. Sheet metal is slit and stretched at right angles to form an expanded metal lattice.
• the lattice typically has diamond shaped openings.
• the lattice has a Long Way of Diamond (LWD) dimension, measured across the long axis of the diamond, between centers of opposing metal joints between openings, and a Short Way of Diamond (SWD) dimension, measured across the short axis of the diamond, between centers of opposing metal joints between openings.
• LWD Long Way of Diamond
• SWD Short Way of Diamond
• expanded metals are preferred because they are sufficiently rigid to maintain good electrical contact with the cell housing at the periphery of the catalytic electrode and can have lower electrical resistance than woven screens because of their one-piece structure.
• expanded metals include expanded nickel, expanded nickel plated steel and expanded stainless steel.
• Expanded metal material and dimensions can be selected to provide the desired strength, electrical resistance and open area. For example, increasing the base metal thickness and metal strand width between openings can reduce electrical resistance and increase strength but can increase the volume of the current collector, and the LWD and SWD dimensions can affect the current collector strength and adhesion of the catalytic material.
• the expanded metal can have a base metal thickness from 0.025 mm to 0.255 mm.
• the base metal thickness is preferably at least 0.050 mm and more preferably at least 0.075 mm.
• the base metal thickness is preferably no greater than 0.200 mm and more preferably no greater than 0.125 mm.
• the strand width can be from about 0.025 mm to about 0.255 mm.
• the strand width is preferably at least 0.075 mm and more preferably 15 least 0.100 mm.
• the strand width is preferably no greater than 0.200 mm and more preferably no greater than 0.150 mm.
• the openings in the expanded nickel can have 10 to 100 openings per inch, preferably 20 to 60 openings per inch.
• the LWD and SWD dimensions can each range from about 0.250 mm to about 13.00 mm.
• the LWD and SWD dimensions are preferably at least 0.500 mm and more preferably at least 1.00 mm.
• the LWD and SWD dimensions are preferably no greater than 5.00 mm and more preferably no greater than 3.175 mm.
• Expanded nickel is available as nickel EXMET® from Dexmet Corp., Naugatuck, Connecticut, USA; examples include 4 Ni 5-060 P&L and 3 Ni 3.3-05 EXMET®.
• the coating of electrically conductive particles can include a binder to adhere the conductive particles to the substrate or protective metal surface layer.
• Suitable materials include fluoropolymers such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) and polyvinylidene fluoride (PVDF); other polymers such as polyvinyl alcohol (PVA) and polyurethane (e.g., colloidal dispersed polyurethane); and combinations thereof.
• the particles in the coating can be particles of any electrically conductive material that will provide a rough surface and is relatively resistant to corrosion and dissolution when in contact with the catalytic material and electrolyte.
• Suitable materials include carbons such, as graphite and carbon black, and metals such as gold, tin, silver and nickel; carbons and gold are preferred, with graphite and carbon black being most preferred.
• suitable graphite coating materials include TIMREX® LBlOOO, LB 1016 and LB 1090 aqueous graphite dispersions (TIMCAL America, Westlake, OH, USA), ECCOCOAT® 257 (W. R. Grace & Co.), and ELECTROD AG® 109 and 112 and EB0005 (Acheson Industries, Port Huron, MI, USA).
• the concentration of particles in the coating will be sufficient to provide good electrical conductivity between the catalytic layer and the current collector, and sufficient binder will be used to hold the particles together and adhere the coating to the current collector.
• the coating will contain at least 0.1 weight percent binder and more preferably at least 0.5 weight percent binder.
• the coating will contain no more than 5 weight percent binder and more preferably no more than 2 weight percent binder.
• the coating can be a continuous coating in the general area coated, or it can be a discontinuous coating if uncoated spots within the general area coated leave only the protective metal surface layer exposed.
• a separate protective metal surface layer can be applied by any suitable method. Examples include electroplating, electroless plating and vapor deposition (chemical or physical), sputtering and electroless plating.
• the coating of electrically conductive particles can be applied by any suitable method, such as painting, dipping, spraying, printing and application with a transfer pad.
• the current collector and catalytic electrode can be used in electrochemical cells of various shapes, sizes and internal constructions.
• the cell can be a button cell, a cylindrical cell, a prismatic cell or a flat cell.
• the size and shape of the current collector can vary.
• the counter electrode can contain or use a variety of active materials, depending on the type of cell.
• a fuel cell can use a different fluid from the gas used as the catalytic electrode (e.g., hydrogen, methanol or ethanol); and a metal-air cell, air-assisted cell, hydrogen generating cell or oxygen generating cell can use a metal such as zinc, lithium, aluminum or magnesium as an active material.
• the aqueous alkaline electrolyte can contain a solute such as potassium hydroxide and/or sodium hydroxide in a water-based solvent.
• a solute such as potassium hydroxide and/or sodium hydroxide in a water-based solvent.
• Various additives can also be included in the electrolyte, such gelling agents, performance enhancing materials such as zinc oxide, and indium compounds, surfactants and other materials to reduce the generation of gas from undesirable corrosion reactions.
• FIG. 3 is a cross-sectional drawing of an embodiment in which the cell is a prismatic shaped metal-air cell with an aqueous alkaline electrolyte that has a counter electrode containing a metal as the negative electrode active material and a catalytic electrode, such as the embodiment in FIG. 1 , that uses oxygen contained in the air from outside the cell as the positive electrode active material.
• the cell 1 10 includes a positive electrode (cathode) casing 112 and a negative electrode (anode) casing 126. At least one hole 1 18 is present in the bottom of cathode can 112 to act as an air entry port.
• the cathode casing is preferably formed of nickel-plated steel.
• the anode casing 126 has a rim 135 is flared outward at its open end.
• the anode casing can have essentially straight side walls and a rim with little or no outward flare, or can have a rim folded outward and back along the side wall to form a substantially U-shaped side wall with a rounded edge at the open end of the casing.
• the anode casing 126 can be formed from a single layer of material such as stainless steel, mild steel, cold rolled steel, aluminum, titanium or copper, or it can include one or more additional layers of material to provide good electrical contact to the exterior surface of the anode casing 126, resistance of the external surface to corrosion, and resistance to internal cell gassing where the internal surface of the anode casing 126 comes in contact with the anode 128 or electrolyte, such as a three-layered (triclad) material such as nickel/stainless steel/copper.
• a three-layered (triclad) material such as nickel/stainless steel/copper.
• a catalytic positive electrode such as air electrode 120 is disposed near the bottom of the cathode casing 112 of the cell 110.
• Electrode 120 includes a catalytic layer 121, which can contain a mixture of a conductive material such as a carbon, a catalyst, and a binder.
• Air electrode 120 preferably has a hydrophobic air diffusion layer 122, such as a hydrophobic membrane or film, which can be laminated thereon.
• the hydrophobic layer 122 is on the side of the air electrode closest to the bottom of the cell when oriented as shown in FIG. 3 (the port side of the electrode).
• Air electrode 120 also includes an electrically conductive current collector 123 as described above.
• the air electrode may also contain a barrier membrane 137, such as a PTFE film, between the hydrophobic layer 122 and a central region 1 14 of the bottom of the cathode casing 1 12.
• a barrier membrane 137 such as a PTFE film
• PTFE films that can be used include thermomechanically expanded PTFE membranes, such as EXCELLERATORTM Gas Diffusion Membranes from W. L. Gore and Associates and TETRATEXTM PTFE membranes from Donaldson Membranes, and other microporous PTFE films, such as N6389A PTFE film from Performance Plastics Products (3P). Expanded films can provide higher gas transmission rates than non-expanded films.
• the cell 1 10 has a negative electrode that contains an anode mixture 128 including a metal such as zinc and an aqueous alkaline electrolyte containing potassium hydroxide and/or sodium hydroxide for example.
• the electrolyte and/or anode mixture can also contain additional ingredients such as zinc oxide and organic compounds.
• the anode mixture 128 preferably includes zinc powder, electrolyte solution, a binder such as CARBOPOL® 940, and gassing inhibitor(s) such as indium hydroxide (In(OH) 3 ) and DISPERB YK® D 190 (an anionic polymer and is available from Byk Chemie of Wallingford, Connecticut) and zinc oxide.
• Preferred zinc powders are low-gassing zinc compositions suitable for use in alkaline cells with no added mercury. Examples are disclosed in U.S. Patent Nos. 6,602,629 (Guo et al), 5,464,709 (Getz et al.) and 5,312,476 (Uemura et al), which are hereby incorporated by reference.
• a low-gassing zinc is ZCA grade 1230 zinc powder from Zinc Corporation of America, Monaca, PA, USA, which is a zinc alloy containing about 400 to about 550 parts per million (ppm) of lead.
• suitable zinc alloys include product grades NGBIA 100, NGBIA 115, and BIA available from N. V. Umicore, S. A., Brussels, Belgium.
• Cell 110 also includes a gasket 130 made from an elastomeric material which serves as a seal between the cathode casing 112 and the anode casing 126.
• a sealant may be applied to the sealing surface of the gasket, cathode casing and/or anode casing.
• examples include asphalt, either alone or with elastomeric materials or ethylene vinyl acetate, aliphatic or fatty polyamides, and thermoplastic elastomers such as polyolefins, polyamine, polyethylene, polypropylene and polyisobutene.
• a suitable tab (not shown) can be placed over the openings 118 and removed when the cell 110 is ready for use to keep air from entering the cell 110 before use.
• PP534 type prismatic air metal-air cells were made using air electrodes containing one of two different catalysts, with vs. without gold plated current collectors. All cells had a negative electrode containing zinc powder as the active material and an aqueous potassium hydroxide electrolyte.
• the current collectors were made from 3 Ni 3.3-05P expanded metal; the current collectors in Lots A and C were not plated, and the current collectors in Lots B and D were plated with gold on essentially all of both the separator side and the port side of the expanded metal; and the current collectors were embedded into the separator sides of the catalytic layers.
• Cells were continuously discharged at a rate of 100 mA/cm 2 , based on the surface area of the air electrode adjacent to the negative electrode. Discharge curves are plotted in FIG. 4, which shows that gold plating on the current collector increased the voltage for cells with both types of catalysts.
• Air convection was provided to the test electrodes so the test results would not be limited by the amount of air available to the electrode during the test.
• the limiting current current at 1.05 V vs. zinc
• the average limiting current and the average maximum power are summarized in Table 1.
• Adhesion of the catalytic material to the gold plated current collector was observed to be improved when a graphite coating was added over the gold plating, and there was generally a desirable increase in limiting current and maximum power with a graphite coating. While adhesion of the catalytic material appeared to be best when both sides of the current collector was coated with graphite, surprisingly the limiting current and the maximum power were better when only the separator side of the current collector was coated with graphite. In general, limiting current and maximum power were better with the 4 Ni 5-060 P&L expanded metal than with the 3 Ni 3.3-05 expanded metal.
• Electrodes without a PTFE film layer were made from each current collector lot and tested for adhesion of the catalytic material to the current collector, using a pressure test in which a sample piece of electrode was mounting in a clamping device with a 0.635 cm (0.250 inch) opening on both sides of the sample and air pressure applied to the separator side of the electrode sample was gradually increased (at a rate of about 70.3 g/cm 2 (1 pound per square inch) per second), until there was an audible "pop" sound and the gauge pressure dropped to zero, indicating that the bond between the catalytic material and the current collector had broken.
• Table 2 These results show that adhesion was substantially improved when the current collector is coated with graphite. Adhesion was best when both sides of the current collector were coated with graphite, but even coating just one side provided a significant improvement over uncoated current collectors, both with and without gold plating.
• Electrodes were tested for alternating current (AC) impedance in half cells flooded with potassium hydroxide electrolyte solution vs. a zinc reference electrode, at open circuit potential, with a peak to peak alternating potential amplitude of 10 mV applied over a frequency range from 100 KHz to 0.1 Hz.
• the electrode impedance at 65 KHz is summarized in Table 2.
• Plating the current collector with gold generally resulted in lower electrode impedance, both with and without graphite coating.
• Gold plating and graphite coating of the current collector each resulted in a higher limiting current.
• the improvement was not as great as with an uncoated, gold plated current collector.
• the best results were achieved with a gold plated current collector coated with graphite on only the separator side, so that a portion of the gold plating was in contact with the catalytic material.
• Electrodes from each lot were tested in half cells flooded with aqueous potassium hydroxide electrolyte vs. a zinc reference electrode as described in Example 2. The results are summarized in Table 2. The results are similar to those for electrode impedance. [0055] PP534 type prismatic zinc-air cells were made using electrodes from each lot. Negative electrodes containing zinc powder and the electrolyte was an aqueous potassium hydroxide solution.
• Electrodes and cells with palladium plated current collectors had limiting currents that were at least as high as electrodes and cells with gold plated current collectors. Table 3

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